Communications system

ABSTRACT

A mobile communications system is proposed in which mobile communications devices are arranged to transmit signals to and to receive signals from a base station using one or a subset of available sub-bands, with the base station being configured to move the mobile communications devices between the sub-bands. An anchor sub-band is also provided on which idle mobile communications devices camp until they are moved to one or more other sub-bands in addition to or instead of the anchor sub-band.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/735,012, filed Jan. 6, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/858,889, filed Dec. 29, 2017, now U.S. Pat. No.10,542,532, which is a continuation of U.S. patent application Ser. No.14/875,797, filed on Oct. 6, 2015, now U.S. Pat. No. 9,888,464, which isa divisional of U.S. patent application Ser. No. 13/138,755, filed onSep. 23, 2011, which is a National Stage Entry of InternationalApplication No. PCT/JP2010/057781, filed Apr. 26, 2010, which claimspriority from United Kingdom Patent Application No. 0907180.4, filedApr. 27, 2009. The entire contents of the above-referenced applicationsare expressly incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to communications devices, particularlybut not exclusively devices operating according to the 3GPP standards orequivalents or derivatives thereof. The invention has particular but notexclusive relevance to the impacts of carrier aggregation that is to beused in LTE-Advanced as currently defined in 3GPP standardsdocumentation TR 36.814.

BACKGROUND ART

With LTE Rel 8, a transmission band of 20 MHz was defined. InLTE-Advanced carrier aggregation will be used to support systembandwidths up to 100 MHz. This involves splitting the system bandwidthinto five 20 MHz sub-bands, each centered on a respective componentcarrier. In order to be backwards compatible with LTE Rel 8 UserEquipment (UEs), at least one of those sub-bands has to be LTE Rel 8compliant.

To support carrier aggregation a new Physical Downlink Control Channel(PDCCH), structure is needed to address the aggregated system bandwidthof up to 100 MHz. Two different approaches, separate PDCCH for eachcarrier and common PDCCH for multiple carriers, are under considerationin RAN 1. One of these two methods will be agreed to be adopted for theLTE-Advanced System. Irrespective of this decision, at any given pointin time the UE may not transmit or receive data on all the componentcarriers. The base station (referred to as the eNB in LTE documentation)should have the flexibility to schedule a UE on any of the componentcarriers it wishes and should be able to move the UE on to differentcomponent carriers as required. The UE on the other hand should know inadvance which subset of the component carriers it should monitor andturn off its RP transceiver circuitry for the others. This would resultin considerable power savings in the UE.

DISCLOSURE OF INVENTION

The present invention provides a simple mechanism by which the eNBscheduler can switch the UE among the different component carriers.

According to one exemplary aspect, the present invention provides acommunications device comprising: a transceiver operable to transmitdownlink data to and to receive uplink data from a remote communicationsdevice using a plurality of component carriers; and a controlleroperable to control the transceiver so that the communications devicetransmits broadcast and paging channels on an anchor subset of saidcomponent carriers but not on another subset of the component carriers.

The controller may transmit control data to the remote communicationsdevice instructing the remote device to monitor one or more componentcarriers in the other subset of component carriers. This may be inaddition to or instead of monitoring component carriers in the anchorsubset. The controller may also transmit DRX control data to the remotecommunications device to cause the remote device to switch offtransceiver circuits for component carriers that it has not beeninstructed to monitor. The controller may transmit the control datawithin a MAC layer communication message as this is fast and relativelyreliable compared with RRC layer signalling.

The controller may receive a connection request from the remotecommunications device on a component carrier belonging to the anchorsubset and in response transmits downlink data for the remotecommunications device on a different component carrier. Before sendingthe downlink data, the controller would inform the remote communicationsdevice of the component carriers it will use to carry the downlink data.

The present invention also provides a communications device comprising:a transceiver operable to transmit uplink data to and to receivedownlink data from a remote communications device on a plurality ofcomponent carriers, wherein an anchor subset of the component carriersinclude broadcast and paging channels; and a controller operable tocontrol the transceiver so that during an idle mode, the communicationsdevice is operable to camp on one or more of the component carriers inthe anchor subset. The communications device can thus receive system andpaging information when in Idle mode.

The controller may receive control data from the remote communicationsdevice instructing the communications device to monitor one or morecomponent carriers in another subset of the component carriers and thecontroller may control the transceiver to monitor the component carriersin that other subset. The controller may also receive DRX control datafrom the remote communications device and which the controller can useto determine when to switch off parts of the transceiver configured forcomponent carriers that are not to be monitored. The control data ispreferably received within as MAC layer communication message.

When the communications device wishes to make a connection, for example,to make a call, the controller may transmit a connection request on thecomponent carrier on which the device is camped and may receive downlinkdata from the remote communications device on a different componentcarrier that the communications device has been instructed to monitor.

In order to save battery power, the controller can switch off parts ofthe transceiver for component carriers on which the communicationsdevice is not camped or is not monitoring.

The present invention also provides a communications device comprising:a transceiver operable to transmit downlink data to and to receiveuplink data from a remote communications device using a subset ofcomponent carriers; and a controller operable to control the transceiverso that: i) daring a first interval the communications device isoperable to communicate with the remote communications device on a firstsubset of component carriers; ii) the communications device transmitscontrol data to the remote communications device using the first subsetof component carriers, the control data instructing the remotecommunications device to communicate with the communications deviceusing a second subset of component carriers; and iii) during a secondinterval the communications device is operable to communicate with theremote communications device on the second subset of component carriers.

The invention also provides a communications device comprising: atransceiver operable to transmit uplink data to and to receive downlinkdata from a remote communications device using a subset of componentcarriers; and a controller operable to: i) control the transceiver sothat during a first interval the communications device is operable tocommunicate with the remote communications device on a first subset ofcomponent carriers; ii) receive control data from the remotecommunications device using the first subset of component carriers, thecontrol data instructing the communications device to communicate, withthe remote communications device using a second subset of componentcarriers; and iii) control the transceiver so that during a secondinterval the communications device is operable to communicate with theremote communications device on the second subset of component carriers.

The invention provides, for all methods disclosed, correspondingcomputer programs or computer program products for execution oncorresponding equipment, the equipment itself (user equipment, nodes orcomponents thereof) and methods of updating the equipment.

An exemplary embodiment of the invention will now be described, by wayof example, with reference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a mobile telecommunication system of atype to which the invention is applicable;

FIG. 2 a schematically illustrates a generic frame structure used incommunications over the wireless links of the system shown in FIG. 1 ;

FIG. 2 b schematically illustrates the way in which the frequencysubcarriers are divided into resource blocks and the way that a timeslot is divided into a number of OFDM symbols;

FIG. 3 schematically illustrates the way in which carrier aggregation isused to provide a system bandwidth of up to 100 MHz;

FIG. 4 illustrates a DRX timing pattern generated by the base stationfor a mobile telephone and used to control when the mobile telephone isasleep and awake;

FIG. 5 schematically illustrates a base station forming part of thesystem shown its FIG. 1 ;

FIG. 6 schematically illustrates a mobile telephone forming part of thesystem shown in FIG. 1 ; and

FIG. 7 is a block diagram illustrating the main components oftransceiver circuitry forming part of the mobile telephone shown hi FIG.6 .

BEST MODE FOR CARRYING OUT THE INVENTION

Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which users of mobile telephones (MT) 3-0, 3-1, and 3-2 cancommunicate with other users (not shown) via one of the base stations5-1 or 5-2 and a telephone network 7. A number of uplink and downlinkcommunications resources (sub-carriers, time slots etc) are availablefor the wireless link between the mobile telephones 3 and the basestations 5. In this exemplary embodiment, the base stations 5 allocatedownlink resources to each mobile telephone 3 depending on the amount ofdata to be sent to the mobile telephone 3. Similarly, the base stations5 allocate uplink resources to each mobile telephone 3 depending on theamount and type of data the mobile telephone 3 has to send to the basestation 5.

In this exemplary embodiment, the system bandwidth is divided into five20 MHz sub-bands, each being carried by a respective component carrier.The base station 5 is operable to allocated resources for each mobiletelephone 3 on one or more of the component carriers, depending on thecapability of the mobile telephone 3 concerned and the amount of data tobe transmitted between the base station 5 and that mobile telephone 3.The mobile telephones 3 have transceiver circuitry that can receive andtransmit signals on the different component carriers and when the mobiletelephone 3 is not scheduled to use a particular component carrier, itcan power down the corresponding transceiver circuitry to conservebattery power.

LTE Sub-Frame Data Structure

Before discussing the specific ways in which the base station 5schedules the different mobile telephones 3, a description will be givenof the access scheme and a general frame structure agreed for LTE Rel 8.An Orthogonal Frequency Division Multiple Access (OFDMA) technique isused for the downlink to allow the mobile telephones 3 to receive dataover the air interface with the base station 5. Different sub-carriersare allocated by the base station 5 (for a predetermined amount of time)to each mobile telephone 3 depending on the amount of data to be sent tothe mobile telephone 3. These are referred to as physical resourceblocks (PRBs) in the LTE specifications. PRBs thus have a time andfrequency dimension. To do this, the base station 5 dynamicallyallocates PRBs for each device that it is serving and signals theallocations for each sub-frame (TTI) to each of the scheduled mobiletelephones 3 in a control channel,

FIG. 2 a illustrates a generic frame structure agreed for LTE Rel 8communications over the air interface with the base station 5. As shown,one frame 13 is 10 msec long and comprises ten sub-frames 15 of 1 msecduration (known as a Transmission Time Interval (TTI)). Each sub-frameor TTI comprises two slots 17 of 0.5 msec duration. Each slot 17comprises either six or seven OFDM symbols 19, depending on whether thenormal or extended cyclic prefix (CP) is employed. The total number ofavailable sub-carriers depends on the overall transmission bandwidth ofthe system. The LTE specifications define parameters for systembandwidths from 1.4 MHz to 20 MHz and one MB is currently defined tocomprise 12 consecutive subcarriers for one slot 17. A PRB over twoslots is also defined by the LTE specifications as being the smallestelement of resource allocation assigned by the base station scheduler.These sub-carriers are then modulated onto a component carrier toup-convert the signal to the desired transmission bandwidth. Thetransmitted downlink signal thus comprises N_(BW) subcarriers for aduration of N_(symb) OFDM symbols. It can be represented by a resourcegrid as illustrated in FIG. 2 b . Each box in the grid represents asingle sub-carrier for one symbol period and is referred to as aresource element. As shown, each PRB 21 is formed from 12 consecutivesub-carriers and (in this case) seven symbols for each subcarrier;although in practice the same allocations are made in the second slot 17of each sub-frame 15 as well.

At the start of each sub-frame 15, the base station 5 transmits a PDCCH23 (Physical Downlink Control Channel) over the first three symbols. Theremaining symbols form the PDSCH 25 (Physical Downlink Shared Channel)which is used to carry the downlink user data for the mobile telephones3. The PDCCH channel includes, among other things, data for each of themobile telephones 3, indicating if the mobile telephone 3 is scheduledfor receiving downlink data in that sub-frame or is scheduled for uplinktransmission in that sub-frame; and if so, data identifying the PRBs tobe used for receiving the downlink data or for transmitting the uplinkdata.

LTE-Advanced

In the proposed LTE-Advanced system, a number of separate sub-bands willbe provided in order to support wider transmission bandwidths, each ofthe sub-hands will at least be similar in structure to the LTE structurediscussed above. The sub-carriers for each sub, hand will be modulatedonto a separate component carrier so that the transmitted sub-bands arecontiguous or non-contiguous with each other. This is known as carrieraggregation and is schematically illustrated in FIG. 3 for fivesub-bands 25-11 to 25-5, each being 20 MHz wide, giving a total systembandwidth of 100 MHz. In the following description, the terms sub-bandand component carrier will be used interchangeably.

Although LTE-Advanced mobile telephones 3 will support bandwidths up to100 MHz, they may not transmit/receive in the whole spectrum at anygiven time. In order to allow the mobile telephones 3 to save batterypower the system is preferably arranged so that the mobile telephones 3monitor one or a subset of the component carriers to start with; andthen the base station scheduler, based on the activity of the mobiletelephone 3, can direct the mobile telephone 3 to monitor a different(although perhaps overlapping) subset of the component carriers.

If all component carriers (sub-bands 25) are configured as LTE Rel 8compatible, then full system information and paging would be broadcaston each component carrier. However the inventor considers this to be awaste of system resources. The inventor has realised that since allthese component carvers belong to one cell (of base station 5) there isno real benefit in putting the paging and broadcast information in eachof the component carriers (sub-bands 25). The inventor thereforeproposes that only one or a subset of the component carriers in the cellshould carry broadcast and paging information. In this exemplaryembodiment, one component carder (sub-band 25) carries this systeminformation and it will be referred to as the anchor or primary carriercomponent. This is illustrated in FIG. 3 , which shows that sub-band25-3 is the anchor carrier component and it carries the broadcast andpaging information for the cell. Thus, all mobile telephones 3 will campon this anchor carrier component when in the Idle mode and will read thesystem and paging information from it.

Release 8 mobile telephones 3 will only be scheduled on one of theanchor carrier components as they will have the same structure asdefined for LIE Release 8. For an LTE-Advanced mobile telephone 3, sinceit will be camped on the anchor carrier component of the cell when Idle,the inventor proposes that such a mobile telephone 3 would initiate theRRC Connection Establishment Procedure on the anchor carrier componentwhen it wants to snake a connection (for example to make a call). Oncethe RRC Connection or an EPS bearer is established, the base station 5can then instruct the mobile telephone 3 to move to one or moredifferent component carriers at a suitable instance. This helps inbalancing the load among the different component carriers within thecell and reduces battery consumption in the mobile telephone 3 as themobile telephone only has to monitor a subset of the carrier componentstogether with the anchor carder component.

The base station 5 can signal which of the component carriers the mobiletelephone 3 should monitor and on which the mobile telephone 3 shouldtransmit/receive data, by:

-   -   PDCCH Signalling    -   MAC Signalling    -   RRC Signalling.

In all three cases an Information Element (IE) will be needed that willbe 5 bits long, with each bit corresponding to one of the componentcarriers and identifying whether or not the mobile telephone 3 shouldmonitor the corresponding component carrier.

PDCCH Signalling: Signalling a mobile telephone 3 which componentcarrier it should monitor through PDCCH is the fastest technique.However, it is also the most unreliable (as no acknowledgement is sentby the mobile telephone 3 back to the base station 3 to acknowledgereceipt of the information). PDCCH signalling can be achieved bysignalling a special PDCCH format with a 5-bit bitmap indication foreach mobile telephone 3 in sub-frame. (n−1), indicating that the mobiletelephone 3 should start listening to the component carriers for whichthe bit is set to “1” from sub-frame (n) onwards, until a further changeis signalled.

MAC Signalling: Signalling each mobile telephone 3 which componentcarriers it should monitor through a MAC Control element is fast andfairly reliable. It could be achieved, for example, by having an LE inthe DRX Command MAC Control Element, with a 5-bit bitmap indication foreach mobile telephone 3, indicating that the mobile telephone 3 shouldstart listening to the corresponding component carriers for which thebit is set to “1”. The base station 5 can then assume that the mobiletelephone 3 has applied the new configuration once it has received theacknowledgement that the mobile telephone 3 has received the DRX CommandMAC Control Element.

RRC Signalling: RAC layer Signalling each mobile telephone 3 whichcomponent carriers it should monitor through an RRC message would beslow but very reliable. However, as the component carriers that a mobiletelephone 3 may monitor might change frequently, RRC signaling is notpreferred for this purpose.

Therefore, in this embodiment, MAC Signalling is used for indicating toeach mobile telephone 3 which component carriers it should monitor. Asthey will not monitor or transmit/receive data on the other componentcarriers, LTE-Advanced mobile telephones 3 can switch off theirtransceiver circuitry for the component carriers they will not monitor.

DRX Handling

LTE Rel 8, each mobile telephone 3 can be configured to receive and/ortransmit data in discontinuous time periods, the duration and frequencyof which are controlled by the base station 5. This discontinuousreception/transmission is called DRX/DTX and allows the mobile telephone3 to turn off its transceiver circuitry during the periods when it isnot supposed to receive data from and/or transmit data to the basestation 5, thereby reducing power consumption. The base station 5defines the DRX pattern such that the mobile telephone 3 remains awakefor the on-duration and monitors PDCCH and then goes to sleep. Thisconcept is illustrated in FIG. 4 .

A similar although more complex DRX procedure can be used to controlLTE-Advanced mobile telephones 3 so that they switch off theirtransceiver circuitry for component carriers they are not monitoringeven during the defined “On-Duration”. Indeed there are two possibleways of configuring DRX for LTE-Advanced mobile telephones.

Alternative 1: The same basic LTE Rel-8 mechanism is used forLTE-Advanced, with certain modifications to keep the system simple andbackwards compatible. In particular, a two level DRX configuration canbe used. On the first level one DRX configuration (On Duration, RXCycle) is configured by the RRC layer of the base station 5 for themobile telephone 3 (identical to what is defined for LTE Rel 8). On thesecond level, during the “On-Duration” the mobile telephone 3 willmonitor the component carriers indicated by the MAC control element (DRXCommand MAC Control Element). Hence even during the on-duration the UEwill monitor only those carriers that are actually needed to bemonitored and can switch off its transceiver circuitry for receiving theother carriers. This will provide considerable savings in battery life.

When the mobile telephone's activity increases, the mobile telephone 3will start transmitting/receiving on an increased number of componentcarriers but the “On duration” would remain unchanged. If the mobiletelephone 3 is already transmitting/receiving on all the componentcarriers and if there is a further increase in activity, then the basestation 5 can increase the On-duration defined for that mobile telephone3.

Alternative 2 Another alternative is to have one DRX configuration percomponent carrier (On Duration, DRX Cycle). In this case the mobiletelephone 3 would perform a Boolean “OR” of the DRX configurations forall the component carriers to determine the overall DRX pattern definingwhen the mobile telephone 3 should be awake and asleep; and would usethe individual DRX configurations to control the switching off of thetransceiver circuitry for the non-monitored component carriers duringthe awake periods. However, battery savings in the mobile telephone 3will be less with this alternative if the DRX cycles and the startinginstances of the On Durations for the component carriers are not timealigned. Hence a better way would be to have the same DRX cycle for allcomponent carriers but with different On Durations. This would also workif the DRX cycle for one or more of the component carriers is an integermultiple of the DRX cycle of the other component carriers.

Base Station

FIG. 5 is a block diagram illustrating the main components of each ofbase stations 5 shown in FIG. 1 . As shown, each base station 5 includestransceiver circuit 31 which is operable to transmit signals to and toreceive signals from the mobile telephones 3 via one or more antennas 33and which is operable to transmit signals to and to receive signals fromthe telephone network 7 via a network interface 35. A controller 37controls the operation of the transceiver circuit 31 in accordance withsoftware stored in a memory 39. The software includes, among otherthings, an operating system 41 and a communications control module 43having a resource allocation module 45 and a scheduler module 47. Thecommunications control module 43 is operable to control the generationof the sub-frames in the different sub-bands 25 in which the uplink anddownlink data is transmitted from/to the mobile telephones 3. Theresource allocation module 45 is operable for allocating the resourceblocks in the different sub-bands 25 to be used by the transceivercircuit 31 in its communications with each of the mobile telephones 3,depending on the amount of data to be transmitted between the basestation 5 and the mobile telephones 3. The scheduler module 47 isoperable to schedule the times for the transmission of the downlink datato the mobile telephones 3 and the times for the mobile telephone 3 totransmit its uplink data to the base station 5. The communicationscontrol module 43 is responsible for signalling, to each of the mobiletelephones 3, data identifying which component carriers the mobiletelephone should be monitoring when in the Idle mode; and for moving themobile telephones 3 between the different component carriers when in RRCConnected mode; and for defining the DRX patterns used for controllingthe times when the mobile telephones 3 can switch off its transceivercircuitry.

Mobile Telephone

FIG. 6 is a block diagram illustrating the main components of each ofthe mobile telephones 3 shown in FIG. 1 . As shown, the mobiletelephones 3 include transceiver circuit 71 that is operable to transmitsignals to and to receive signals from the base station 5 via one ormore antennas 73. As shown, the mobile telephone 3 also includes acontroller 75 which controls the operation of the mobile telephone 3 andwhich is connected to the transceiver circuit 71 and to a loudspeaker77, a microphone 79, a display 81, and a keypad 83. The controller 75operates in accordance with software instructions stored within a memory85. As shown, these software instructions include, among other things,an operating system 87 and a communications control module 89 thatincludes a resource allocation module 91 and a transceiver controlmodule 93. The communications control module 89 is operable to controlcommunications with the base station 5 and during the Idle mode monitorsthe anchor component carrier 25-3. The resource allocation module isresponsible for identifying the resources on which uplink should betransmitted and on which downlink data is to be received in thedifferent sub-bands 25. The transceiver control module 93 is responsiblefor identifying the parts of the transceiver circuit 71 that can beswitched off at the current instance using, for example, DRXconfiguration data received from the base station 5 or using knowledgeof the sub-bands 25 that the mobile telephone 3 is to monitor.

In the above description, the base station 5 and the mobile telephones 3are described for ease of understanding as having a number of discretemodules (such as the resource allocation modules, scheduler module,transceiver control module etc). Whilst these modules may be provided inthis way for certain applications, for example where an existing systemhas been modified to implement the invention, in other applications, forexample in systems designed with the inventive features in mind from theoutset, these modules may be built into the overall operating system orcode and so these modules may not be discernible as discrete entities.

As mentioned above, LTE-Advanced mobile telephones 3 have transceivercircuit 71 that can transmit and receive data on a number of differentcomponent carriers. FIG. 7 is a block diagram illustrating suitabletransceiver circuit 71 that may be used. As shown, the transceivercircuit 71 includes five up-converter/down-converter circuits 95-1 to95-5, one for each of the five sub-bands 25, for modulating anddemodulating the sub-carriers onto the corresponding component carrier(C1 to C5). The transceiver circuit 71 also includes fiveencoding/decoding circuits 97-1 to 97-5 for encoding and decoding theuplink data and downlink data respectively in each of the five sub-bands25. The encoding/decoding circuits 97 receive the uplink data from, andpass the decoded downlink data to, the controller 75. The controller 75also supplies individual power control signals (via the dashed signallines) to the encoding/decoding circuits 97 and to the up-convertercircuits 95, so that individual circuits can be powered down when notneeded and so that they can all be powered down when none of thecircuits are needed (for example when the mobile telephone 3 enters itssleep mode).

Modifications and Alternatives

A detailed embodiment has been described above. As those skilled in theart will appreciate, a number of modifications and alternatives can bemade to the above embodiment whilst still benefiting from the inventionsembodied therein. By way of illustration only a number of thesealternatives and modifications will now be described.

In the above embodiment, a mobile telephone based telecommunicationssystem was described. As those skilled in the art will appreciate, thesignalling and power control techniques described in the presentapplication can be employed in any communications system. In the generalcase, the base stations and the mobile telephones can be considered ascommunications nodes or devices which communicate with each other. Othercommunications nodes or devices may include user devices such as, forexample, personal digital assistants, laptop computers, web browsers,etc.

In the above embodiments, a number of software modules were described.As those skilled will appreciate, the software modules may be providedin compiled or un-compiled form and may be supplied to the base stationor to the mobile telephone as a signal over a computer network, or on arecording medium. Further, the functionality performed by part or all ofthis software may be performed using one or more dedicated hardwarecircuits. However, the use of software modules is preferred as itfacilitates the updating of base station 5 and the mobile telephones 3in order to update their functionalities. Similarly, although the aboveembodiments employed transceiver circuitry, at least some of thefunctionality of the transceiver circuitry can be performed by software.

Various other modifications will be apparent: to those skilled in theart and will not be described in further detail here.

The following is a detailed description of the way in which the presentinventions may be implemented in the currently proposed 3GPP LTEstandard. Whilst various features are described as being essential ornecessary, this may only be the case for the proposed 3GPP standard, forexample due to other requirements imposed by the standard. Thesestatements should not, therefore, be construed as limiting the presentinvention in any way.

INTRODUCTION

To support carrier aggregation a new PDCCH structure is needed toaddress up to 100 MHz of aggregated system bandwidth. Two differentapproaches, separate PDCCH for each carrier and common PDCCH formultiple carriers, are under consideration in RAN 1. One of the methodswill be agreed to be adopted for LTE Advance System. Irrespective ofthis decision, at any given point in time the UE may not transmit orreceive data on all the component carriers. eNB scheduler should havethe flexibility to schedule a UE in any of the component carrier itwishes and should be able to move it around. The UE on the other handshould know in advance which subset of the component carriers it shouldmonitor and turn of the RP for the others. This would result inconsiderable power savings in UEs.

In this contribution we discuss the simple mechanism by which the eNBscheduler could switch the UE would among different component carriers.

DISCUSSION

In LTE Advance system we would see Carrier aggregation, where two ormore component carriers are aggregated in order to support widertransmission bandwidths e.g. up to 100 Mhz and for spectrum aggregation.These carrier aggregations could be contiguous or non-contiguous.Although LTE Advanced UEs will support 100 MHz BW however it may nottransmit/receive in the whole spectrum at any given time. In order toenable the UE to save battery power it would be wise that the UE listensto only some of the component carriers to start with and then the eNBscheduler, based on the activity of the UE can direct it to monitorsubset of component carriers.

4.1. Idle Mode Camping

If all component carriers are configured as R8 compatible, the fullsystem information and paging should be broadcast on each componentcarrier. However we see this as wastage of the resources. We think sinceall these component carrier belongs to one cell there may not be anybenefit for putting the paging and broadcast information in each of thecomponent carrier. We suggest that there should be only a subset of thecomponent carrier in the cell that carries broadcast and paginginformation and we call this carrier component as the Anchor or PrimaryCarrier Component as shown in FIG. 3 . This would also mean that theIdle mode UE will camp on this Anchor Component and shall read thesystem and paging information from it.

4.2 UE in Connected Mode

Release 8 UE will only be scheduled on the Anchor Carriers as they havethe same structure as the LTE Release 8.

For Release 9, since the UE will be camped on the Anchor CarrierComponent of the cell we would suggest that it would be logical that theUE would initiate RRC Connection Establishment Procedure on the AnchorCarrier Component. Once the RRC Connection or an EPS bearer isestablished the, UE shall be instructed by the network to move on to thedifferent component carrier at a suitable instance. This will help inbalancing the load among different carriers within the cell andreduction in LTE battery consumption as the UE would only monitor asubset of the carrier components together with the anchor carriercomponent.

Proposal 2: There should be a mechanism available through which the UEshould be moved around the different component carriers.

Signalling of which component carriers the UE will monitor andtransmit/receive the data on can be done by

-   -   PDCCH Signalling    -   MAC Signalling    -   RRC Signalling.

In all the three cases we would need an IE that would be 5 bit long witheach bit corresponding to a component carrier which the UE shouldmonitor.

PDCCH Signalling: Signalling the UE which component carrier it shouldmonitor through PDCCH is the fastest although it is unreliable. We couldhave a special PDCCH format with 5 bits bitmap indication to the UE insub frame (n−1) that it should start listening to the component carriersfor which the bit is set to 1 from sub frame a onwards until furtherchange is signaled.

MAC Signalling: Signalling the UE which component carrier it shouldmonitor through MAC Control element is fast and fairly reliable. Wecould have an IE in the DRX Command MAC Control Element with 5 bitsbitmap indication to the UE that it should start listening to thecomponent carriers for which the bit is set to 1. eNB will assume thatthe UE has applied the new configuration after it has received theacknowledgement from the UE.

RRC Signalling: RRC layer Signalling the UE which component carrier itshould monitor through in a RRC message would be slow and although veryreliable. As the component carriers a UE may monitor may changefrequently RRC signaling may not be a suited for this purpose.

Hence our preference would be to use MAC Signalling for indicating theUE which component carriers it should monitor.

Proposal 3 a MAC Signalling be Used to Indicate to the UE which CarrierComponent it should Monitor

Further there is no point in the UE monitoring all the carriers as theUE would not be transmitting or receiving on these carriers. Moreover,since the retransmissions will be performed on the respective HARQentities for each carrier, hence it makes sense that UE switches off theRF Circuitry of the Component carriers it is not monitoring.

Proposal 4 UE Could be Configured to Monitor the Anchor Carrier and aSubset of the Carriers.

4.3. DRX Handling

In Rel 8 we have a DRX defined such that the LTE remains awake for theon-duration and monitors PDCCH and then goes to sleep. This concept isshown in FIG. 4 .

We can two possible ways of configuring DRX for LIE Advance.

Alternative 1 We can still keep the basic Rel-8 mechanism for LTEadvance with certain modification and keep the system simple andbackward compatible. We can have a 2 level DRX configuration in LTE. Onthe first level we will have only one DRX configuration (On Duration,DRX Cycle) configured by RRC for the UE, identical to what we had it inRelease 8. On the second level, during the “On-Duration” UE will monitorthe carriers indicated by the MAC control element (DRX Command MACControl Element). Hence even during the on-duration the UE will monitoronly those carriers that are actually needed to be monitored and canswitch off the RF Circuit for receiving the other carriers. This willprovide considerable saving in battery life.

When the UE activity increases, the UE will start transmitting/receivingon the increased number of component carriers but the On duration wouldremain unchanged. If UE is already transmitting/receiving on of thecomponent carriers and if there is a further increase in the activity,the on-duration will be increased.

Alternative 2 Another general alternative is to have the one DRXconfiguration per component carrier (On Duration, DRX Cycle) and the UE“ORs” the DRX configuration per component carrier to determine other theoverall DRX pattern. However, battery savings in the UE will be less incase DRX Cycles and the starting instance of the On Duration of thecomponent carriers are not aligned. Hence a better way would be to havethe same DRX cycle on all component carrier with a different onduration.

Also the DRX cycle in one component carrier could be a integral multipleof DRX cycle on the other component carrier.

CONCLUSIONS

In this paper we discuss how the UE in the idle and connected mode beassigned to monitor a subset of carriers. The main proposal of thecontribution are

-   -   Proposal 1: Idle mode UE will camp on Anchor Component and shall        read the system and paging information from it    -   Proposal 2; There should be a mechanism available through which        the UE should be moved around the different component carriers    -   Proposal 3; MAC Signalling be used to indicate to the UE which        carrier component it should monitor    -   Proposal 4 UE could be Configured to monitor the Anchor Carrier        and a subset of the Carriers.

We request RAN 2 to discuss this and NEC would be happy to draft a textproposal for the TR to capture the agreements in the TR.

This application is based upon and claims the benefit of priority fromUnited Kingdom Patent Application No. 0907180.4, filed on Apr. 27, 2009,the disclosure of which is incorporated herein in its entirety byreference.

The invention claimed is:
 1. A method for a user equipment (UE), themethod comprising: performing communication of a plurality of componentcarriers including a primary component carrier and at least onesecondary component carrier; receiving a Medium Access Control (MAC)control element including a bitmap, each bit of at least part of thebitmap corresponding to one of the at least one secondary componentcarrier; wherein the bitmap indicates that the UE is to monitor data onat least one secondary component carrier corresponding to at least onebit among the bitmap set to “1”; and monitoring the data on the primarycomponent carrier and the at least one secondary component carriercorresponding to the at least one bit among the bitmap set to “1”.
 2. Auser equipment (UE) comprising: a memory storing instructions; and atleast one processor configured to process the instructions to: toperform communication over a plurality of component carriers including aprimary component carrier and at least one secondary component carrier;to receive a Medium Access Control (MAC) control element including abitmap, each bit of at least part of the bitmap corresponding to one ofthe at least one secondary component carrier, wherein the bitmapindicates that the UE is to monitor data on eat least one secondarycomponent carrier corresponding to at least one bit among the bitmap setto “1”; and monitor the data on the primary component carrier and the atleast one secondary component carrier corresponding to the at least onebit among the bitmap set to “1”.
 3. A method for a base station, themethod comprising: performing communication over a plurality ofcomponent carriers, including a primary component carrier and at leastone secondary component carrier; and sending a Medium Access Control(MAC) control element to a user equipment (UE) including a bitmap, eachbit of at least part of the bitmap corresponding to one of the at leastone secondary component carrier; wherein the MAC control element isconfigured with each bit of the bitmap, corresponding to the one of theat least one secondary component carrier that the UE is to monitor data,respectively set to “1”, and wherein the data is monitored by the UE onthe primary component carrier and the one of the at least one secondarycomponent carrier corresponding to the at least one bit among the bitmapset to “1”.
 4. A base station comprising: a memory storing instructions;and at least one processor configured to process the instructions toperform communication over a plurality of component carriers including aprimary component carrier and at least one secondary component carrier;send a Medium Access Control (MAC) control element to a user equipment(UE) including a bitmap, each bit of at least part of the bitmapcorresponding to one of the at least one secondary component carrier;and wherein the MAC control element is configured with each bit of thebitmap, corresponding to the one of the at least one secondary componentcarrier that the UE is to monitor, respectively set to “1”, and whereinthe data is monitored by the UE on the primary component carrier and theone of the at least one secondary component carrier corresponding to theat least one bit among the bitmap set to “1”.